Driven by the potential applications of CNTs with unique electrical and mechanical properties, intensive research effort has been dedicated to assembling CNTs into various bulk materials. For example, CNT sheets (bucky paper) represents one of the most attractive CNT bulk materials, and is considered by some as an alternative to indium tin oxide (ITO) for transparent electrically conductive electrodes. CNT spun fibers can combine both high strength and high stiffness derived from individual CNTs. The vertically aligned CNT forest has found important applications in field emission displays and flexible energy storage devices.
Among various CNT bulk materials, CNT aerogels represent a new material that integrates the merits of CNTs with their intriguing intrinsic properties and aerogel with their unique structure and related properties. Aerogels are attractive in various applications owning to their highly porous structure, low bulk density, and large specific surface area. While their composition varies from silica, metal oxides and polymers to carbon based materials, aerogels allow a wide range of applications including, but not limited to, thermal and acoustic insulating materials, catalyst support, and electrodes for supercapacitors.
CNT aerogels are conventionally produced through extracting the liquid component out of a wet gel that was prefabricated from a precursor solution by a solution-processed approach. Due to the difficulties in dispersing CNT with appropriate dispersants, fabrication of CNT aerogels is challenging with only few reported successful examples. During the process of producing CNT sheets and drawing nanotube fibers, aerogels were produced as intermediate phases, which are not free-standing monoliths, and eventually collapse into dense structures. Only one free-standing CNT aerogel has been reported to have been fabricated through a solution-processed approach, in which CNT aerogel was derived from a CNT wet gel formed by sodium dodecylbenzene sulfonate (NaDDBS) dispersed CNTs. Due to the low mechanical strength of the CNT aerogel obtained, poly vinyl alcohol (PVA) was incorporated for reinforcement, which undesirably decreased the electrical conductivity and increased the density of the aerogel.